What is the "boundary of our Solar System"?

Some things, like a table or a soccer field have clear edges and boundaries. Other things, like cities and towns, have boundaries that aren’t as easy to see. It is hard to say where they end and something else begins if you are looking at them from a distance.

Our Solar System has a boundary – but where is it? You could say that the Solar System extends as far as the influence of the Sun. Could the reach of the Sun’s light or the extent of the Sun’s gravity help us decide how far the Solar System extends? The light from the Sun gets fainter as you move farther away, but there is no specific place where the light stops or where it suddenly weakens. Also, the influence of the Sun’s gravity extends without limit, although it is weaker the farther away from the Sun that you travel. There is no boundary at which either light or gravity stops. Neither of these would seem to help us define our Solar Systemís "edge."

The heliosphere helps define one type of boundary of our Solar System. The solar wind from our Sun blows outward against the material between the stars, called the interstellar medium, and clears out a bubble–like region. This bubble that surrounds the Sun and the Solar System is called the heliosphere. It is a definable, measureable region in space.

IBEX is the first spacecraft designed to collect data across the entire sky about the heliosphere and its boundary. Scientists have used this data to make the first maps of our heliosphere boundary. Our heliosphere boundary does not emit light that we can detect, which means it would be impossible to image using conventional telescopes. Instead of collecting light, like other telescopes do, IBEX collects particles coming from the boundary so that we can learn about the processes occurring there. The boundary of the Solar System protects us from harmful cosmic rays. Without it, four times more cosmic rays would enter our Solar System and potentially damage our ozone layer and DNA. It is important to study this region to know how it works.

An artistís rendition of our heliosphere, showing the outward-flowing solar wind and the various boundary regions.